Data propagating on networks continuously increase the mass thereof, and the transmission speed of the network is inevitably further accelerated. Concurrently with this stream, an optical module/device implemented within the optical communication system resultantly enhances operational speed thereof. Recent receiver optical modules may operate over 40 Gbps, and sometimes requested to operate at 100 Gbps. Such high speed operation, a receiver optical module often has architecture of, what is called, the wavelength multiplexed system.
A receiver optical module applicable to the wavelength multiplexed signal installs a plurality of photo-detectors and an optical de-multiplexer to de-multiplex the wavelength multiplexed signal into respective optical signals dependent on wavelengths. Various types of optical de-multiplexers have been proposed in the field. Japanese Patent laid open Nos. JP2007-003812A, JP2002-040283A, JP2004-133114A, and JP2009-198576A have disclosed such modules to receive the wavelength multiplexed signal.
When conventional optical de-multiplexers such as disclosed in the prior arts above listed are applied to an optical signal that multiplexes eight (8) or more signal components, the number of wavelength selective filter (hereafter denoted as WSF) corresponding to the number of the signal components are required. Those WSFs have respective filter performance specific thereto, for instance, respective filters are necessary to have specific transmitting (or reflecting) performance different from others, which drastically raises a cost of the module. Moreover, continuous requests for an optical module applicable to the optical communication system are to make the size of the module in compact. One type of optical transceivers that installs a receiver optical module for the wavelength multiplexed signal has a width of only 7 mm. It would be so hard to install a receiver optical module installing a plurality of WSFs, inevitably, a widened optical de-multiplexer in such a slimed optical transceiver. The present application is to provide an optical de-multiplexer with a narrowed width even when the de-multiplexer enables to de-multiplex more than 8 signals.